Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Basis of Presentation
Fair value of assets, Transfers from Level 1 to Level 2	$ 0		$ 0	$ 0	$ 0
Fair value of assets, Transfers from Level 2 to Level 1	0		0	0	0
Fair value of liabilities, Transfers from Level 1 to Level 2	0		0	0	0
Fair value of liabilities, Transfers from Level 2 to Level 1	0		0	0	0
Fair value of liabilities, Transfers into (out of) Level 3	0		0	0	0
Fair value of assets, Transfers into (out of) Level 3	$ 0		$ 0	$ 0	$ 0
Percentage of employees purchase of common shares at discount price		15.00%

No definition available.

Name:	tmc_BasisOfPresentationAbstract
Namespace Prefix:	tmc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

No definition available.

Name:	tmc_FairValueAssetsLevel1ToLevel2TransfersAmount1
Namespace Prefix:	tmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

No definition available.

Name:	tmc_FairValueAssetsLevel2ToLevel1TransfersAmount1
Namespace Prefix:	tmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

No definition available.

Name:	tmc_FairValueLiabilitiesLevel1ToLevel2TransfersAmount1
Namespace Prefix:	tmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of transfers of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

No definition available.

Name:	tmc_FairValueLiabilitiesLevel2ToLevel1TransfersAmount1
Namespace Prefix:	tmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the percentage of employees purchase of common shares at discount price.

No definition available.

Name:	tmc_PercentageOfEmployeesPurchaseOfCommonSharesAtDiscountPrice
Namespace Prefix:	tmc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

No definition available.

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy.

No definition available.

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration